Water absorption by amaranth grain in plain water was determined at 30, 40, 50 and 60 degreesC by recording the weight increase in grain with respect to time. Water absorption kinetics at these temperatures was described by the Fick's second law solution for diffusion out of sphere. Effective diffusion coefficients varied between 2.63 and 8.25 x 10(-12) m(2)/s for the range investigated. The activation energy for diffusion obtained was 32.1 kJ mol(-1). The rates of absorption in SO2 aqueous solution (0.01%, 0.02% and 0.03%, v/v) were slightly higher than in plain water at 40 and 60 degreesC. However, the increase in SO2 concentration did not seem to increase significantly water absorption. Amaranth grain soaked in 0.02% (v/v) SO2 aqueous solution and variable lactic acid concentrations (0.0025% and 0.0050%, v/v) was performed at 40 degreesC. Absorption rates for lactic acid concentrations were higher than those steeped only in SO2 aqueous solution; lactic acid concentration had no effect on the absorption rate. The amount of total solids leached in sulfur dioxide solution with lactic acid (200 ppm SO2 + 0.005% lactic acid) was the highest when compared with the other steeping media investigated. (C) 2003 Elsevier Ltd. All rights reserved.